# Comparative Analysis of Annealing–Dissolution Techniques for Hollow Submicron Metal Oxide Fiber Synthesis

## TL;DR

Researchers created hollow metal oxide fibers using electrospinning and ALD, comparing two methods to remove the polymer core, which affects the fiber's structure and potential uses.

## Contribution

The study introduces a controllable method to tailor fiber morphology by selecting polymer removal techniques, enabling enhanced surface area for practical applications.

## Key findings

- Thermal annealing produces smooth, shrunken fibers, while water dissolution creates rough, expanded fibers with micro-cracks.
- The rough and expanded fibers have a higher specific surface area, suitable for sensing, catalysis, and filtration.
- The polymer removal method critically influences the final structural and morphological characteristics of the fibers.

## Abstract

Double-shell ZnO/Al2O3 submicron hollow fibers were successfully fabricated through a combined electrospinning and atomic layer deposition (ALD) approach. Polyvinyl alcohol (PVA) fibers were first produced by electrospinning and subsequently coated with a conformal Al2O3 barrier layer via low-temperature ALD employing trimethylaluminum (TMA) and deionized (DI) H2O to preserve the integrity of the temperature-sensitive polymer core. The inner polymer was then removed using two different techniques—thermal annealing and water dissolution—to compare their effects on the fiber morphology. Finally, a functional ZnO layer was deposited by thermal ALD with diethylzinc (DEZ) and DI H2O. It was found that the polymer removal method critically determined the final structural and morphological characteristics of the fibers. Thermal annealing resulted in smooth, shrunken fibers, while water dissolution led to diameter expansion and the formation of a highly rough, bubble-like surface structure due to swelling-induced micro-cracking. The selection of the polymer removal method offers a precise and controllable route for tailoring the fiber morphology. The resulting high-aspect-ratio (HAR) structures, particularly the rough and expanded fibers, exhibit enhanced specific surface area, making them highly promising for applications in sensing, catalysis, and filtration.